In dental treatment, various tooth restorative materials are being used. For example, in restoring the tooth damaged by decay, breakage or the like, pasty restorative composite materials for filling, generally called composite resin are in wide use. This composite resin ordinarily comprises a polymerizable monomer, a filler, a photopolymerization initiator, etc. and is photo-curable. With this composite resin, the restorative operation of tooth is simple and the tooth after restoration is beautiful.
The pasty composite resin comprising a photopolymerization initiator is required to hardly cure in an environmental light until it is used. Further, the pasty composite resin, when used, is required to be cured rapidly by strong light application using a light applicator or the like. However, any of conventional composite resins has had no sufficiently good balance between the stability to environmental light and the high reactivity to applied light. That is, there has been developed yet no pasty composite resin which causes no cure by a weak light such as environmental light and is cured rapidly by a strong light of light applicator or the like.
In order to solve the above problem, the present inventors made studies on novel photopolymerization initiators. As the result of the studies, the present inventors found a photopolymerization initiator comprising an α-diketone compound, a photoacid generating agent and an amine compound and proposed it (Patent Documents 1 and 2). Incidentally, as the amine compound, there is preferably used an aromatic amine from the standpoints of the high polymerization activity, etc.
The photopolymerization initiator developed by the present inventors is not activated when irradiated with a weak light (e.g. an environmental light) (below 1 mW/cm2 at 360 to 500 nm), whereby a pasty composite resin comprising this photopolymerization initiator is protected from polymerization. Meanwhile, when irradiated with a strong light by a light applicator such as halogen lamp, xenon lamp or the like, the pasty composite resin completes polymerization in a very short time. The composite resin containing the photopolymerization initiator is cured rapidly when irradiated with a strong light, and the cured material obtained has good properties. Therefore, the photopolymerization initiator enables production of a dental composite resin having good properties.
In restoration of tooth by using a conventional dental composite resin, it is generally possible to conduct a restoration in which the restored site harmonizes with neighboring teeth in such an extent that the site is difficult to distinguish and the restored site is beautiful. However, the restored site looks blackish in an environment where an ultraviolet light or a visible light of short wavelength is applied, and the person having a restored tooth is forced to have a mental burden.
In order to alleviate this drawback, it was proposed to compound a fluorescent agent in a dental composite resin. As the fluorescent agent compounded, a phthalate ester fluorescent agent is easy to procure, emits a fluorescence similar to natural teeth, and gives an excellent beauty. Therefore, this fluorescent agent is being used advantageously (see, for example, Patent Document 3).    Patent Document 1: JP2005-89729A    Patent Document 2: JP2005-213231A    Patent Document 3: National Publication of International Patent Application-2002-520347